1. Field of the Invention
This invention relates to ammonothermal growth of group-III nitrides.
2. Description of the Related Art
Ammonothermal growth of group-III nitrides, for example, GaN, involves placing, within a reactor vessel, group-III containing source materials, group-III nitride seed crystals, and a nitrogen-containing solvent, such as ammonia, sealing the vessel and heating the vessel to conditions such that the vessel is at elevated temperatures (between 23° C. and 1000° C.) and high pressures (between 1 atm and, for example, 30,000 atm). Under these temperatures and pressures, the nitrogen-containing solvent may become a supercritical fluid which normally exhibits enhanced solubility of the group-III containing materials into solution. The solubility of the group-III containing materials into the nitrogen-containing solvent is dependent on the temperature, pressure and density of the solvent, among other things. By creating two different zones within the vessel, it is possible to establish a solubility gradient where, in one zone, the solubility will be higher than in a second zone. The group-III containing source materials are then preferentially placed in the higher solubility zone and the seed crystals in the lower solubility zone. By establishing fluid motion of the solvent with the dissolved source materials between these two zones, for example, by making use of natural convection, it is possible to transport the fluid from the higher solubility zone to the lower solubility zone where the group-III nitride crystals are grown on the seed crystals.
What is need in the art are improved techniques for ammonothermal growth of group-III nitrides. The present invention satisfies this need.